Copier system

ABSTRACT

An element responsive to the level of reflected light scans a document in consecutive parallel scan lines, producing an electrical output signal which is converted from analog to digital form. The digital output is entered into one of a pair of storage resistors. A copy of the document is produced by a multihammer helix printer which composes one line of dots at-a-time by printing plural line segments simultaneously. The hammers are energized so as to press against the helical bar in accordance with the outputs of corresponding digital-to-analog converters connected respectively to parallel output lines from the storage registers. A transfer switch control causes one register to be in the output mode operating the hammers while the other is in the input mode for serial data entry, and vice versa on alternate scan lines.

United States Patent 1191 Potter May 28, 1974 l l COPIER SYSTEM [75]Inventor: John T. Potter, Locust Valley, N.Y.

[73] Assignee: Potter Instrument Company Inc., Plainview, NY.

[22] Filed: May 25, 1972 [21] Appl. No.: 256,965

Related US. Application Data [63] Continuation-impart of Ser. No.136,950, April 23,

[58] Field of Search 178/30, 71.13, 5,17, 17 D, 178/17 R, 17 S, 5.4 E,5.4 ES, DIG. 27, 25, 7.1 E, 6.6 R, 7.1; 346/74 ES, 75

OTHER PUBLICATIONS Character Recognition, M. H. Glauberman, Electronic,pp. 132-136, Feb. 1956.

Character Selection for Mosaic Printer," J. Mako, 1MB, Vol. 4, No. 5,Oct. 1961, p. 6.

Primary Examiner-Thomas A. Robinson Attorney, Agent, or Firm-Laurence J.Marhocfer [57] ABSTRACT An element responsive to the level of reflectedlight scans a document in consecutive parallel scan lines, producing anelectrical output signal which is converted from analog to digital form.The digital output is entered into one of a pair of storage resistors. Acopy of the document is produced by a multi-hammer helix printer whichcomposes one line of dots at-a- [56] References Cited time by printingplural line segments simultaneously. UNlTED STATES PATENTS The hammersare energized so as to press against the 2,618,702 11/1952 Thompson 17871 E helical bar accordance with the outputs of 2,930,847 3/1960 Metzger178/30 1 9 9 dlgltal'to'analog cPnveflers Connected 3,174,427 3/1965Taylor 178/30 spectlvely to parallel Output 111168 from the Storage3,233,037 2/1966 F611 178/5 s- A t ns er switch control causes oneregister to 3,465,360 9/1969 Hackley et a1. 346/74 ES be in the outputmode operating the hammers while 3,512,158 6/1970 Scarbrough t 178/30the other is in the input mode for serial data entry, 3,609,759 9/I97ITeske 6! 8|. I78/I7 and vice versa on alternate an line 3,622,70111/1971 Gardner 178/30 3,723,646 3 1973 Behfllle 81 al. 346/74 ES 15Claims, 3 Drawing Flgules /LOGIC UN1T8O FROM COPY LIMIT TRANSDUCER 88 92FROM 84 COUNTER ZOOO PULSE IREV RESET TRANSDUCER 86 STORAGE UNIT 64 1 1FROM A D 94 l l l l l l l l l l iiz'glNELvERLlNEs TO g-AR 7 PR E-AMR 1seggon 2 68 f lllllllll 78 oi STORAGE UNIT 66 M FROM.

X E Z T PULSE/REV l swlTcH I FROM TRANSDUCER 9s QONTRQL lPULSE/REV.

TRANSDUCER 72 PATENIEBIIII 28 I974 3.813.492 SHEET 1 BF 2 FROM PRINTER IP/REV 0 38 PAPER FEEDB TRANSDUCER 72 FAST MOTOR 40 iBfis IE STEP ZGENERATOR Mom R 30 as Q50 "57 H 0728 p 12-34 COPY LI IT 36 SIGNAL TO 88LOGIC UNIT so 8? [EL Is4- P/REV SCANIED COPY 90 N 5 HEL'X PR'NTER'Z' TOS.W.96 CLAM PED TO DRUM 9 86 5 M4 3 J 74 V m I-I- 2000 P/REV. I 72 TOLOGIC UNIT so ELI X 6/ \so 44{M0T0R 4 s2 46/ 52 4s HAMM E R c0I\ITR0Is6- FIRI- s 56 292? CIRCUIT FEED 54 56 l -5 DIGITAL T0 ANALOG D A 58CONVERTER couv. cow CONV.

ROM STORAGE UNITS .66 VIA SWITCHES 94 PATENTEDIU 28 m4 SHEET 2 BF 2fLOGI C UNIT 80 FROM COPY LIMIT o TRANSDUCER as 94 F/ 6. 2.

92 FROM a4 2000 PULSE /REV COUNTER HRESET TRANSDUCER as 60 STORAGE UNIT64 76 I 78 94 FROM A D I 94 I I I I l I I I I, l TWELVE LINES To D-ASENSORPREAMP v ONVERTERS 58 F R 22 es ITITIITTI 78HAMMERS 4s I I im-rs II STORAGE uNlTss I se FROM |54 I; PULSE/REV SWITCH I FROM TRANSDUCER 9aQ IPULSE/REV. TRANsDUcER 72 s'roRAeE UNIT 64 I [I02 I I I STAGE STAGE II 1 #I2 I 7 l I I I I04 I FROM AD I I 16 corgv. 62I STAGE STAGE l I VIA3 SWITCH ee #4 I I I -I L INPUT I |os I I I STAGE STAGE I I I I I2 I l II I I O O FDR HAMMER|2 FOR HAMMER#I w I TO DA CONVERTERS 58 VIA SWITCHES94 COPIER SYSTEM CROSS REFERENCE TO RELATED APPLICATION This applicationis a continuation-in-part of copending application Ser. No. 136,950,entitled Facsimile Printing System, filed on Apr. 23, 1971 by John T.Potter and assigned to the assignee of this application.

BACKGROUND OF THE INVENTION The invention relates generally to opticalscanning and copier systems, and more particularly to improved systemsfor controlling the operation of an electromechanical printer inresponse to the output of an optical scanning system.

Unlike most photographic or xerographic copiers, the copier, orfacsimile system of the instant invention first scans the originaldocument with a light level sensor to produce electrical signals whichdrive a dot printer. The dot printer'reproduces the original, one narrowline at-a-time.

The mechanical and electrical elements of improved helical bar facsimileprinter are disclosed in the aforementioned copending application Ser.No. 136,950. Briefly, that printer comprises a continuously rotatinghelical bar with a plurality of convolutions and a correspondingplurality of hammer blades aligned in parallel with the helix axis.Paper and inked ribbon are carried between the bar and hammer blades.Dots are printed by individually impelling the hammer blades against thebar. As the bar rotates the points where the helical bar and hammersintersect are continuously and repeatedly advanced along a line in eachline segment. An entire line is thus composed by printing a plurality ofline segments simultaneously.

While the multi-hammer helix printer operates at much higher speed thansingle-bladed, lawn mower type helix printers, scanning of the originaldocument is complicated by the fact that the print line is divided intoa plurality of simultaneously printed segments. In the past, specialscanning systems were designed for scanning corresponding line segmentsof the original document simultaneously. In particular, in theaforementioned copending application, Ser. No. 136,950, the originaldocument is scanned with a plurality of equally spaced photocells ridingon a linear track. Each cell is simultaneously moved over a segment ofthe line corresponding to a particular hammer in the printer. In acopending application Ser. No. 178,211, filed Sept. 7, 1971, entitled"Optical Line Scanner and Facsimile System assigned to the same assigneeas this application, a video tube scanning system is disclosedrepresenting another technique for simultaneous scanning of plural linesegments. Mechanical systems employing photocells do, however, have anadvantage over video systems: photocells cost less, are inherentlycapable of higher resolution and have an output which is easier totransmit. However, if a single photocell is swept over an entire line,the electrical output is serial; that is, the output represents thelight level point-by-point along the entire length of the scan line. Theserial signals are therefore not in the proper form for operating amultihammer helix printer.

SUMMARY OF THE INVENTION Accordingly, the general purpose of theinvention is to improve scanning systems and control circuits associatedwith multi-hammer, simultaneous line segment, facsimile printers.Another object of the invention is to enable the output of a singlephotosensor scanning system to drive a multi-hammer facsimile printer byreorganizing the output so that it corresponds with the line segmentsprinted by each hammer. A further object of the invention is to employdigital techniques to enable a multi-hammer helix printer to print dotswith a plurality of discrete levels of darkness representing thetonality of corresponding points in the original document.

These and other objects of the invention are achieved by employing apair of alternated storage registers into which digital signalsrepresenting the analog output of a single photosensor are seriallyentered and then read out in parallel fashion to the hammer drivecircuits of a multi-hammer helix printer. The original document isfastened to the surface of a continuously rotating scan drum. Thephotosensor is moved step-wise along a linear track extending parallelto the axis of the drum such that the document is scanned inconsecutive, parallel sweeps. The helix printer includes a continuouslyrotating helical bar and a plurality of hammer blades aligned parallelto the axis of the bar such that each hammer blade corresponds to anadjacent helical convolution. Paper and ink ribbon are carried betweenthe helical bar and the aligned hammer blades. The paper is advanced oneline at a time in a direction perpendicular to the helix axis. Thestep-wise advancement of the photosensor corresponds to the movement ofthe paper in the printer. The output of the photosensor is digitized inan analog-to-digital converter. The converter output is alternatelypassed on corresponding cycles of the rotating helical bar to the serialinput of either one of the pair of storage registers. Theanalog-to-digital converter and storage register are gated or clockedduring input at a rate corresponding to the number of print positionsalong the entire print line. For example, in one embodiment the helixprinter employs 12 hammers having 154 dot print positions for eachhammer resulting in 1,848 print positions along the entire print line.Accordingly, the analog input to the converter is regularly sampled1,848 times per cycle of the scan drum. Similarly, each storage registermust provide 1,848 bits of storage per output bit of theanalog-todigital converter.

Each storage register is tapped to provide a plurality of paralleloutput lines to the hammer drive circuits in the printer. In the aboveembodiment each storage register would provide 12 parallel output linesper converter output bit. After the digital information for one completescanning cycle is stored in one of the registers, that register isswitched to the output mode in which the stored bits corresponding toconsecutive print positions are clocked past each of the hammer outputlines at a rate corresponding to the number of dot print positions perhammer during each cycle of the helical bar. While one storage registeris in the output mode the other storage register is in the input modereceiving digital information from the next scanning cycle. Adigital-to-analog converter and hammer drive circuit are associated witheach hammer in the helix printer. Corresponding output lines from thestorage register in the output mode are connected to thedigital-to-analog converters which cause the hammer blades to be firedwith variable impact corresponding A BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic and block diagram illustrating the scanningapparatus and helix printer employed in the facsimile system accordingto the invention.

FIG. 2 is a block diagram illustrating the electronic circuitry whichreceives the output of the photosensitive element and reorganizes theinput signals in digital form to provide outputs to drive the helixprinter of FIG. I.

FIG. 3 is a block diagram illustrating one of the storage registers ofFIG. 2 in more detail for an embodiment in which the converted analogoutput of the photosensitive element is coded in three bits.

DESCRIPTION or THE PREFERRED EMBODIMENT In FIG. 1 the scanning apparatusprovides an electrical analog output representing the reflected lightlevel of an original document along a pluralityof parallel'scan lines. Ahelix printer l2 reproduces the original document, that is, creates afacsimile thereof, in response to the electrical output of the scanningapparatus 10 by printing a plurality of dots of varying darkness alongprint lines which correspond to the scan lines along which the originaldocument is read. The scanning apparatus 10 includes a rotatablecylindrical drum 14. The original document is affixed to the surface ofthe drum by means of suitable clamps (not shown). The clamp spaceoccupies only a small portion of the circumference of the drum. Aphotosensor carriage assembly 16 is mounted for linear travel along atrack 18 adjacent to the drum surface and extending parallel to the drumaxis. The carriage assembly 16 houses a high intensity lamp 20 and aphotosensor 22 which is optically aligned with a converging lens 24. Theelectrical output of the photosensor 22 represents the intensity oflight reflected from the focal point of the lens 24 within the areailluminated by the lamp 20. The carriage 16 is movable along the track18 by means of a taut cable 26 passing over a drive capstan 28 and apulley 30 at opposite ends of the track 18. A stepping motor 32 drivesthe capstan 28 which imparts motion to the cable 26 and carriage 16. Thecapstan 28 may be mounted directly on the shaft of the stepping motor32. When pulsed, the motor 32 provides an incremental, lineardisplacement or step of the carriage 16. The travel of the carriage 16during one step should correspond to the motion of the paper in theprinter 12, as explained below. A pair of limit switches 34 and 36 arelocated at opposite ends of the track 18. The switches 34 and 36 operatea switch 38 which alternately connects the stepping motor 32 to a sourceof paper feed pulses and a source of fast return pulses 40. For example,if the scanning proceeds from left to right as viewed in FIG. 1, whenthe carriage 16 engages the limit switch 34, the switch 38 willdisconnect the stepping motor 32 from its normal pulse signal to thefast return pulse generator 40 so that the carriage I6 is quicklyreturned to its original position. After a series of closely spacedpulses from the fast return pulse generator 40, the carriage 16 engagesthe limit switch 36 which causes the switch 38 to return to its normalposition for providing the stepping motor 32 with more widely spacedpulses during the next scanning operation.

The mechanical elements of the printer 12 are similar to those describedin detail in the above-referenced copending application, Ser. No.136,950. The printer 12 comprises a cylindrical drum 42 which is drivencontinuously at high speed by a motor 44 in close proximity to a row ofhammers 46 aligned along a line parallel to the rotational axis of thedrum 42. The motor 44 is also mechanically coupled to drive the drum 14of the scanning apparatus 10 at the same speed, although interconnectedscanning and printing drums are not essential as explained below. Theembodiment of the printer 12 herein described has twelve hammers,although only four are shown in FIG. 1, for convenience of illustration.A helical bar 48 on the cylindrical surface of the drum 42 extendsaround the drum in one complete convolution for each hammer 46. Eachhammer 46 comprises a blade 50 positioned so that its edge will strikethe helical bar 48 when the hammer is actuated. Each blade 50 spans onlyone convolution of the helical bar 48 so that when the hammer isactuated, the blade will strike the bar 48 at only one point. Each ofthe hammers 46 includes a light weight electrical coil 52 affixed toeach respective blade 50. The coils 52 are in a constant magnetic fieldprovided by a permanent magnet field structure (not shown). To actuateeach hammer 46, a firing pulse is applied to the coil 52 which drivesthe associated blade against the helical bar 48.

Paper on which the printing is carried'out and an ink or carbon ribbon(not shown) are positioned between the blades 50 and the drum 42 so thatwhen an actuated hammer blade is impelled against the bar 48, a dot willbe printed on the paper at the intersection of the blade and the helicalbar. As the drum 42 rotates, the intersection of the bar 48 and eachblade 50 will move repeatedly from left to right across the blade. Asthe intersection progresses in one pass by a blade 50, the hammer can beactuated repeatedly to print a selected pattern ofdots along the linecorresponding to the edge of the hammer blade. This line, extended alongall of the blade edges is referred to as the print line. It is importantto note that corresponding intersections of the blades 50 and respectiveconvolutions of the bar 48 occur simultaneously along the length of thedrum 42. For example, if twelve spaced dots are to be printed byrespective blades 50 at corresponding locations along each blade, theblades will all be fired at once.

The print paper is advanced perpendicularly to the drum axis as theprinting is carried out so that parallel lines of dot patterns areprinted. The print paper is advanced through the printer 12 by means ofa paper feed motor 54. The motor 54 causes the paper to be advancedthrough the printer one line per revolution of the drums 42 and 14. Thesame pulses which activate the paper feed motor 54 also activate thestepping motor 32 so that the photosensor carriage 16 and the paper inthe printer are advanced synchronously at the end of each completerevolution of the print drum 42 and scan drum 14.

Associated with each hammer blade assembly 46 is a hammer firing circuit56 which produces the current pulses for the coil 52. Twelvedigital-to-analog converters 58 provide respective outputs to the hammerfiring circuits 56.

The inputs to the digital-to-analog converters 58 corresponding to the12 hammer blades are produced by a signal processing system, as shown inFIG. 2, which is responsive to the output of the photosensor 22 of FIG. 1. The output of the photosensor 22 is passed via a pre-amplifier 60to an analog-to-digital converter 62 which samples and converts theanalog output of the pre-amplifier 60 at a pre-determined rate. A pairof identical storage units 64 and 66 are provided for storing the outputof the analog-to-digital converter 62. Each storage unit 64, 66 iscomprised of shift registers. The number of shift registers in eachstorage unit corresponds to the number of parallel output lines of theconverter 62. The output of the converter 62 may be connected via aswitch 68 to the serial data input of either storage unit 64 or 66. Theswitch 68 is operated by a transfer switch control 70 responsive to theoutput of a transducer 72 arranged adjacent to an index wheel 74connected for rotation with the print drum 42. The transducer 72provides one pulse per revolution of the print drum 42. The switchcontrol 70 reverses the switch 68 once per revolution, causing theoutput of the converter 62 to be routed on one cycle to the storage unit64 and on the subsequent cycle to the storage unit 66. The storage units64 and 66 have clock pulse input terminals 76 and 78 respectively. Alogic unit 80 provides a pulse output which gates the analog-todigitalconverter 62 and provides a clock pulse input to the storage units 64and 66. The storage units 64 and 66 are alternated. While one storageunit is in the input mode, the other storage unit is in the output mode,and vice versa on alternate cycles of the drum 42. The clock pulses fromthe logic unit 80 are passed to either storage unit 64 or 66 via aswitch 82 also controlled by the transfer switch control 70.Accordingly, during one cycle of the scan drum l4 and print drum 42,when the output of the converter 62 is connected via the switch 68 tothe serial input of the storage unit 64, the clock pulses from the logicunit 80 are received at the terminal 76 via the switch 82. During thiscycle, then, the output of the converter 62 will be entered seriallyinto the storage unit 64. Serial entry of the output of the converter 62into the other storage unit 66 is accomplished in a similar manner onthe next cycle after the switches 68 and 82 have been thrown to theiralternate positions by the switch control 70 between the two adjacentcycles.

The logic unit 80 includes a two-input AND gate 84. One input to gate 84is from a transducer 86 arranged adjacent to an index wheel 87 connectedfor rotation with the scan drum 14. The transducer 86 provides 2,000pulses per revolution of the scan drum 14. The other input to the ANDgate 84 is from a copy limit transducer 88. The transducer 88 includes afixed photocell arranged to receive light reflected from a narrow strip90 about one end of the scan drums surface. The strip 90 has a darkenedsection corresponding to the clamp space on the scan drum. Accordingly,the output of the copy limit transducer 88 has two levels. The output ofthe transducer 88 will be a logic zero during the interval correspondingto the clamp space and a logic one during the remainder of the cycle.Thus, the output of the AND gate 84 in the logic unit 80 will be a pulsetrain interrupted once per cycle during the interval corresponding tothe clamp space. The logic unit 80 has a second two input AND gate 92.One input to the AND gate 92 is the output of the AND gate 84. The otherinput to the gate 92 is provided by the output of a counter 94responsive to the pulse output of the AND gate 84. The counter 94 isimplemented to provide a logic one output until 1,848 pulses have beencounted during one cycle, at which time the output of the counter 94falls to the logic zero state. Accordingly, the output of the AND gate92 will be a pulse train of 1,848 pulses per cycle of the scan drum 14.These 1.848 pulses from the logic unit 80 serve to gate the converter 62and to shift the storage unit 64 or 66 during the input mode 1,848 timesper cycle of the scan drum 14.

The logic unit 80 and analog-to-digital converter 62 cooperate to dividethe scan line, that is one circular pass of the photosensor 22 over thecircumference of the drum (except for the clamp space), into 1,848points or units. In the helix printer 12, the print line consists of1,848 dot positions. Each dot position corresponds to a point along thescan line at which the converter 62 sampled the analog output of thephotosensor 22. The 1,848 dot positions are distributed over the 12hammers 46. Each hammer must therefore be capable of printing 154 dotsto compose a line segment. The 154 dot positions per hammer correspondto respective angular orientations of the print drum 42 because theangular position of the drum 42 determines the point of intersection ofa convolution of the helical bar 48 and its corresponding hammer blade50.

The storage units 64 and 66 provide twelve sets of parallel output lineseach to the digital-to-analog converters S8 of the helix printer 12. Thereason why the outputs of the storage units 64 and 66 are in parallelinstead of serial form is because the helix printer 12 composes a printline in parallel or simultaneous line segments rather than in a seriesof dots from one end to the other of the entire print line. Although thehelix printer 12 prints all 12 line segments simultaneously, thescanning apparatus 10 reads a scan line in a serial manner. Therefore,each storage unit 64, 66 must reorganize the digitized input signalsoriginated by the photosensor 22 for operating the printer 12. A set ofganged switches 94, only three of which are shown for convenience ofillustration, alternately connect the outputs of the two storage units64 and 66 to respective digital-to-analog converters 58 of the helixprinter 12. Each switch 94 is a symbolic representation of a pluralityof switches, as each of the twelve sets of output lines ordinarilyincludes several individual leads corresponding to binary digits. In thecondition illustrated in FIG. 2, the storage unit 66 is in the outputmode in which its parallel output lines are connected to the converters58 of the printer 12. At the same time, the storage unit 64 is in theinput mode in which data from the converter 62 is loaded serially intothe storage unit by means of the clock pulses from the logic unit 80. Onthe next cycle of the scan drum 14, the roles of the storage units 64and 66 will be reversed; that is, the storage unit 64 will be in theoutput mode and the storage unit 66 will be in the input mode. Betweencycles, all of the ganged switches 68, 82 and 94 will be thrown to theiralternate positions by means of the switch control in response to theoutput of the one pulse per revolution transducer 72 associated with theprinter 12.

When in the output mode, the storage unit 64 or 66 is clocked at therate of 154 pulses per revolution of the print drum 42 by connecting theclock input 76 or 78 via a switch 96 to a transducer 98 arrangedadjacent to an index wheel 100 connected for rotation with the printdrum 42. The transducer 98 produces 154 output pulses per revolution.The switch 96 is operated by the switch control 70. When the switchcontrol 70 is pulsed, the clock inputs to the storage units 64 and 66are interchanged. For example, on the cycle following that depicted inFIG. 2, the output of the logic unit 80 will be connected to theterminal 78 and the output of the transducer 98 would be connected toterminal 76 of the storage unit 64.

In the input mode the storage units receive 1,848 clock pulses per drumcycle. The remaining 152 pulses from the transducer 86 correspond to theclamp space. That is, one line of the document is scanned in less timethan it takes to complete one drum cycle. In the output mode, thestorage units receive 154 clock pulses during a drum cycle. Therefore,the storage units are clocked at an average rate per drum cycle about 12times faster during the input mode than during the output mode.

The analog-to-digital converter 62 may provide as many output bits asdesired. If only one output bit is provided by the converter 62, theconverter will operate as a threshold detector having a single binaryoutput. In this case, each storage unit 64, 66 will comprise a singleshift register of 1,848 bits. In the preferred embodiment, the converter62 provides three parallel output bits. With three bits, the amplitudeof the analog signal may be represented as any one of eight (2) discretelevels, that is from 000 to l l l, inclusive. Accordingly, each storageunit will include three synchroneously operated shift registers. Thedetails of the storage unit 64 used with a three bit converter are shownin FIG. 3. The storage unit 66 is implemented in a similar manner. Thethree line output of the analogto-digital converter 62 is connected viathe switch 68 (FIG. 2) to the serial inputs of three respective shiftregisters 102, 104 and 106 in the storage unit 64. Each shift registeris divided into 12 states corresponding to the hammers 46 of the printer12. Each stage of each register consists of 154 bits. In FIG. 3, onlythe first and twelfth stages of the shift registers are shown forconvenience of illustration. The clock pulse inputs of the three shiftregisters 102, 104 and 106 are all connected in common to the terminal76. During the input mode the clock pulse terminal 76 is connected tothe logic unit 80, and the three line output of the converter 62 ispassed in parallel to the inputs of the shift registers 102, 104 and 106for serial data entry.

After 1,848 bits of information per shift register are stored during onecomplete cycle, the storage unit 64 is switched to the output mode bymeans of the switches operated by the transfer switch control 70. In theoutput mode, the serial data entry inputs of the shift registers aredisconnected and the clock pulse output terminal 76 is connected to thetransducer 98 associated with the printer 12. As shown in FIG. 3, onlythe last or 154th bit of each stage is tapped for output. The outputsfrom corresponding stages among the shift registers are grouped inthrees corresponding to the respective hammers 46 of the printer 12. Forexample, the outputs from the 154th bit of the 12th stage in shiftregisters 102, 104 and 106 are passed to the digital analog converter 58associated with the twelfth hammer 46. Likewise, the last bits of thefirst stages in the shift registers are passed to the digital-to-analogconverter 58 associated with the first hammer 46.

The contents of each stage are shifted past the tapped bit synchronouslywith the occurrence of the corresponding dot positions along each hammerblade 50 in the printer 12. Following a given shift pulse, the three bitsignal is applied to the respective digital-to-analog converter 58 whichprovides an analog output current through the coil 52 which fires theassociated hammer blade 50 with sufficient impact to print a dot ofcorresponding darkness. After 154 bits have been shifted past eachtapped output bit, the one pulse per revolution transducer 72 activatesthe switch control (FIG. 1) to return the storage unit 64 to the inputmode in which data from the analog-to-digital converter 62 is againserially entered into the three shift registers 102, 104 and 106.

The dot printed by the printer 12 in each of the dot positions along theprint line will have a darkness corresponding to one of eight discretelevels to represent the tonality of the corresponding point on theoriginal copy scanned by the photosensor 22.

As shown in FIG. 1, the print drum 42 and scan drum 14 are mechanicallycoupled so that there is no requirement for electrically synchronizingtheir relative speed or phase. If it were desired to separate thesedrums for facsimile transmission, for example, several synchronizationsystems are available. In one system, a straightforward phased lockedservo-mechanism can be used to control the speed and phase of thescanning drum through the input to its drive motor in response to asignal representing the speed and phase of the print drum 42. Othersystems must be used if the two drum speeds are independent of eachother. In one system, the scanning drum 14 would be run at more thantwice the speed of the printing drum 42. This relationship would alwaysallow enough time to read each line regardless of the phase relationshipbetween the two drums. A scanning or reading cycle would be initiatedafter a given storage register was transferred back to the input mode,but not until the beginning of a copy limit signal appeared. Then, the1,848 samples would be serially entered into the storage register andstored or held until the helical bar 48 returned to the start position.That is, samples would be held for whatever part of an incomplete helixrevolution remained. In this system, the frequency response of thephotosensor 22 would have to be doubled. Another system fornon-phaselocked drums is similar to the foregoing system, except thatthe scanning drum speed would be increased only sufficiently to alwaysexceed the speed of the printing drum 42. Instead of waiting for thecopy limit signal the data from the photosensor 22 would start beingentered into the available storage unit as soon as transfer occurred.Because the start of the scanning cycle would not usually correspond tothe normal starting point of a scan line, that is, the end of the clampspace, additional logic would be required to shift the information inthe storage registers to its proper position. This would require thateach shift register be provided with a number of bits corresponding to2,000 scanning points rather than 1,848. In addition, a loop would haveto be provided to connect the last bit of the shift register to thefirst bit in order to run the bits in storage around until the 152 bitscorresponding to the clamp space were located in the last bits of thestorage register associated with a recognition circuit.

The use of the two alternating storage units 64 and 66 permits theserial output of the scanning apparatus to be reorganized in anefficient manner so that the information printed by the helix printer ]2lags the information scanned by only one cycle. The multi-hammer helixprinter [2 is thus operated as a facsimile printer without reorganizingthe scan line into parallel segments at the scanning end of theoperation. Moreover, the digital storage units facilitate digitalrepresentation of the tonality of the scanned points on the originaldocument. As a result, the helix printer 12 is capable of faithfullyreproducing a graphical representation having areas of varying darknessby printing dots of nonuniform density.

It will be understood that various changes in the details, materials,steps and arrangements of parts which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

I claim:

1. A copier system for reproducing an original copy by composing afacsimile with a plurality of dots of variable darkness, comprisingscanning means including photosensor means for producing an analogelectrical output representing the reflected light level at points onsaid copy and means for causing said photosensor means to scan said copyin consecutive parallel scan lines, converter means operativelyconnected to receive the analog output of said scanning means forconversion thereof to a multi-bit digital output, means for storing saidanalog-to-digital converter means output, digital-to-analog convertermeans operatively connected to receive the output of said storing means,and multi-hammer printer means responsive to said digitalto-analogconverter means output for simultaneously printing a plurality of linesegments along a print line by printing dots of variable darknesscorresponding to the tonality of respective points on said copy forcomposing a facsimile thereof.

2. The copier system of claim 1, wherein said storing means includesstorage register means for serially receiving the output of saidanalog-to-digital converter means and for providing a plurality ofparallel outputs corresponding to the hammers of said printer means, andsaid digital-to-analog converter means includes a plurality ofdigital-to-analog converters operatively associated with respective onesof said hammers for receiving corresponding ones of said paralleloutputs from said storage register means.

3. The copier system of claim 2, wherein said printer means includes ahelical bar having a plurality of convolutions, means for impartingcontinuous rotation to said bar about its axis, a correspondingplurality of hammer blades arranged in a line next to said helical barand parallel to the axis thereof, and a plurality of firing circuitsassociated respectively with said hammer blades for selectivelyimpelling individual ones of said hammer blades against said helical barwith variable impact in accordance with the respective outputs of saiddigital-to-analog converters.

4. A copier system for reproducing an original copy, comprising meansfor scanning said copy in consecutive parallel scans to produce ananalog electrical output representing the level of reflected light fromsaid copy, analog-to-digital conversion means connected to receive theoutput of said scanning means, a pair of digital storage units, meansfor alternately connecting said storage units in an input mode forserial entry of the output of said analog-to-digital conversion means oncorresponding alternate scans, means for alternately connecting saidstorage units in an output mode for providing a plurality of paralleloutputs from said storage units on corresponding alternate scans suchthat one unit is in the output mode while the other unit is in the inputmode, and vice versa on alternate scans, a plurality ofdigital-to-analog conversion means connected to receive respective onesof said parallel outputs from said storage units, and printer meanshaving a plurality of print hammers and respective hammer firingcircuits for impelling said hammers with variable impact in accordancewith the output of said digital-toanalog conversion means.

5. The copier system of claim 4, wherein said printer means furtherincludes a helical bar having a plurality of convolutions correspondingto said hammers, means forimparting continuous rotation to said barabout its axis, said hammers being arranged in a line next to saidhelical bar and parallel to the axis thereof and being impelled againstsaid corresponding helical convolutions when fired.

6. The copier system of claim 5, wherein said scanning means includes asingle photosensitive element and means for causing said element toexecute a plurality of consecutive parallel scans of said copy.-

7. The copier system of claim 6, wherein both said means for alternatelyconnecting are responsive to the rotation of said helical bar forinterchanging said storage units once per complete revolution.

8. A copier system, comprising: a scanning system including a drum uponwhich said original copy is fastened, means for imparting continuousrotation to said drum and a carriage having a light sensitive elementmounted adjacent to the surface of said drum for linear travel in adirection parallel to the rotational axis of said drum such that saidlight sensitive element executes consecutive parallel scans of saidcopy; a helix printer including a helical bar with plural convolutions,means for imparting continuous rotation to said bar about its axis, acorresponding plurality of hammer blades arranged in a line next to saidhelical bar and parallel to the axis thereof for printing simultaneouslya plurality of line segments along a print line, a plurality ofdigital-to-analog converters corresponding to said hammer blades, and aplurality of firing circuits associated respectively with said hammerblades for selectively impelling individual ones of said blades againstsaid helical bar with variable impact in accordance with the output ofrespective ones of said digital-to-analog converters; and a dataconversion system interposed between said scanning system and said helixprinter including an analog-to-digital converter connected to receivethe output of said light sensitive means, a pair of digital storageunits each having a serial data entry terminal, a clock pulse terminaland a plurality of parallel output lines corresponding in number to saidhelix printer hammer blades, input switch means for alternately applyingthe output of said analog-to-digital converter to the serial inputterminals of said storage units, output switch means for alternatelyconnecting each set of parallel outputs associated with said storageunits to the respective inputs of said digital-to-analog converters,clock pulse switch means for applying two different clock pulse ratesalternately to the clock pulse input terminals of said storage units,one said clock pulse rate corresponding to the number of dot printpositions occurring in an entire print line during one complete cycle ofsaid helical bar, the other of said clock pulse rates corresponding tothe number of dot print positions occurring within a line segmentprinted by one of said hammer blades during a complete cycle of saidhelical bar, and transfer switch control means operatively connected tosaid input, output and clock pulse input switch means for reciprocationthereof between respective alternate positions in response to eachcomplete cycle of said helical bar, such that one of said storage unitsis in the input mode clocked at said one rate while the other storageunit is in the output mode clocked at said other rate, and vice versa onalternate cycles.

9. The copier system of claim 8, wherein saidanalogto-digital converterprovidesa plurality of parallel binary outputs and each said storageunit includes a plurality of shift registers corresponding in number tothe outputs of said analog-to-digital converter.

10. The copier system of claim 9, wherein the number of said hammers insaid helix printer is N and there are X dot print positions assigned toeach hammer, each said shift register in each said storage unit beingdivided into N stages, each said stage having X bits of storage, saidparallel output lines from each unit each including one output lineassociated with the last bit in each corresponding stage of said shiftregisters.

11. A method of producing a facsimile of an original 12 copy, comprisingthe steps of scanning said copy in consecutive parallel scan lines toproduce an analog electrical output representing the level of lightreflected from said copy. converting said electrical output to a digitalsignal, storing said digital signal, reconverting the stored digitalsignal to an analog signal, and printing dots of variable darknesssimultaneously in a plurality of line segments along a print line inaccordance with said analog signal.

12. The method of claim 11, further comprising the step of rearrangingsaid stored signal in parallel form corresponding to said line segmentbefore reconverting said stored digital signal to an analog signal.

13. The method of claim 12, wherein said scanning includes continuouslyrotating a scan drum on which said copy is fastened and moving a lightsensitive element adjacent to said scan drum in a direction parallel tothe rotational axis of said scan drum to produce said electrical analogoutput, and said printing is accomplished by continuously rotating ahelical bar and selectively firing against said bar a plurality ofhammers aligned in parallel adjacent to said bar.

14. The method of claim l3, wherein said bar and said scan drum arerotated at the same speed with predetermined relative phase.

15. The method of claim 14, wherein said scan drum is rotated at overtwice the speed of said bar without a predetermined phase relationship.

1. A copier system for reproducing an original copy by composing afacsimile with a plurality of dots of variable darkness, comprisingscanning means including photosensor means for producing an analogelectrical output representing the reflected light level at points onsaid copy and means for causing said photosensor means to scan said copyin consecutive parallel scan lines, converter means operativelyconnected to receive the analog output of said scanning means forconversion thereof to a multi-bit digital output, means for storing saidanalog-todigital converter means output, digital-to-analog convertermeans operatively connected to receive the output of said storing means,and multi-hammer printer means responsive to said digitalto-analogconverter means output for simultaneously printing a plurality of linesegments along a print line by printing dots of variable darknesscorresponding to the tonality of respective points on said copy forcomposing a facsimile thereof.
 2. The copier system of claim 1, whereinsaid storing means iNcludes storage register means for seriallyreceiving the output of said analog-to-digital converter means and forproviding a plurality of parallel outputs corresponding to the hammersof said printer means, and said digital-to-analog converter meansincludes a plurality of digital-to-analog converters operativelyassociated with respective ones of said hammers for receivingcorresponding ones of said parallel outputs from said storage registermeans.
 3. The copier system of claim 2, wherein said printer meansincludes a helical bar having a plurality of convolutions, means forimparting continuous rotation to said bar about its axis, acorresponding plurality of hammer blades arranged in a line next to saidhelical bar and parallel to the axis thereof, and a plurality of firingcircuits associated respectively with said hammer blades for selectivelyimpelling individual ones of said hammer blades against said helical barwith variable impact in accordance with the respective outputs of saiddigital-to-analog converters.
 4. A copier system for reproducing anoriginal copy, comprising means for scanning said copy in consecutiveparallel scans to produce an analog electrical output representing thelevel of reflected light from said copy, analog-to-digital conversionmeans connected to receive the output of said scanning means, a pair ofdigital storage units, means for alternately connecting said storageunits in an input mode for serial entry of the output of saidanalog-to-digital conversion means on corresponding alternate scans,means for alternately connecting said storage units in an output modefor providing a plurality of parallel outputs from said storage units oncorresponding alternate scans such that one unit is in the output modewhile the other unit is in the input mode, and vice versa on alternatescans, a plurality of digital-to-analog conversion means connected toreceive respective ones of said parallel outputs from said storageunits, and printer means having a plurality of print hammers andrespective hammer firing circuits for impelling said hammers withvariable impact in accordance with the output of said digital-to-analogconversion means.
 5. The copier system of claim 4, wherein said printermeans further includes a helical bar having a plurality of convolutionscorresponding to said hammers, means for imparting continuous rotationto said bar about its axis, said hammers being arranged in a line nextto said helical bar and parallel to the axis thereof and being impelledagainst said corresponding helical convolutions when fired.
 6. Thecopier system of claim 5, wherein said scanning means includes a singlephotosensitive element and means for causing said element to execute aplurality of consecutive parallel scans of said copy.
 7. The copiersystem of claim 6, wherein both said means for alternately connectingare responsive to the rotation of said helical bar for interchangingsaid storage units once per complete revolution.
 8. A copier system,comprising: a scanning system including a drum upon which said originalcopy is fastened, means for imparting continuous rotation to said drumand a carriage having a light sensitive element mounted adjacent to thesurface of said drum for linear travel in a direction parallel to therotational axis of said drum such that said light sensitive elementexecutes consecutive parallel scans of said copy; a helix printerincluding a helical bar with plural convolutions, means for impartingcontinuous rotation to said bar about its axis, a correspondingplurality of hammer blades arranged in a line next to said helical barand parallel to the axis thereof for printing simultaneously a pluralityof line segments along a print line, a plurality of digital-to-analogconverters corresponding to said hammer blades, and a plurality offiring circuits associated respectively with said hammer blades forselectively impelling individual ones of said blades against saidhelical bar with variable impact in accordance with the output ofrespective ones of said digital-to-analog converters; and a dataconversion system interposed between said scanning system and said helixprinter including an analog-to-digital converter connected to receivethe output of said light sensitive means, a pair of digital storageunits each having a serial data entry terminal, a clock pulse terminaland a plurality of parallel output lines corresponding in number to saidhelix printer hammer blades, input switch means for alternately applyingthe output of said analog-to-digital converter to the serial inputterminals of said storage units, output switch means for alternatelyconnecting each set of parallel outputs associated with said storageunits to the respective inputs of said digital-to-analog converters,clock pulse switch means for applying two different clock pulse ratesalternately to the clock pulse input terminals of said storage units,one said clock pulse rate corresponding to the number of dot printpositions occurring in an entire print line during one complete cycle ofsaid helical bar, the other of said clock pulse rates corresponding tothe number of dot print positions occurring within a line segmentprinted by one of said hammer blades during a complete cycle of saidhelical bar, and transfer switch control means operatively connected tosaid input, output and clock pulse input switch means for reciprocationthereof between respective alternate positions in response to eachcomplete cycle of said helical bar, such that one of said storage unitsis in the input mode clocked at said one rate while the other storageunit is in the output mode clocked at said other rate, and vice versa onalternate cycles.
 9. The copier system of claim 8, wherein saidanalog-to-digital converter provides a plurality of parallel binaryoutputs and each said storage unit includes a plurality of shiftregisters corresponding in number to the outputs of saidanalog-to-digital converter.
 10. The copier system of claim 9, whereinthe number of said hammers in said helix printer is N and there are Xdot print positions assigned to each hammer, each said shift register ineach said storage unit being divided into N stages, each said stagehaving X bits of storage, said parallel output lines from each unit eachincluding one output line associated with the last bit in eachcorresponding stage of said shift registers.
 11. A method of producing afacsimile of an original copy, comprising the steps of scanning saidcopy in consecutive parallel scan lines to produce an analog electricaloutput representing the level of light reflected from said copy,converting said electrical output to a digital signal, storing saiddigital signal, reconverting the stored digital signal to an analogsignal, and printing dots of variable darkness simultaneously in aplurality of line segments along a print line in accordance with saidanalog signal.
 12. The method of claim 11, further comprising the stepof rearranging said stored signal in parallel form corresponding to saidline segment before reconverting said stored digital signal to an analogsignal.
 13. The method of claim 12, wherein said scanning includescontinuously rotating a scan drum on which said copy is fastened andmoving a light sensitive element adjacent to said scan drum in adirection parallel to the rotational axis of said scan drum to producesaid electrical analog output, and said printing is accomplished bycontinuously rotating a helical bar and selectively firing against saidbar a plurality of hammers aligned in parallel adjacent to said bar. 14.The method of claim 13, wherein said bar and said scan drum are rotatedat the same speed with predetermined relative phase.
 15. The method ofclaim 14, wherein said scan drum is rotated at over twice the speed ofsaid bar without a predetermined phase relationship.